Exploring the solid-form landscape of pharmaceutical hydrates: transformation pathways of the sodium naproxen anhydrate-hydrate system.

Abstract

To understand the transformation pathways amongst anhydrate/hydrate solid forms of sodium naproxen and to highlight the importance of a polymorphic dihydrate within this context. Multi-temperature dynamic vapour sorption (DVS) analysis combined with variable-humidity X-ray powder diffraction (XRPD) to establish the transformation pathways as a function of temperature and humidity. XRPD and thermogravimetric analysis (TGA) to characterise bulk samples. Monitoring of in-situ dehydration using solid-state (13)C CP/MAS spectroscopy. At 25 °C, anhydrous sodium naproxen (AH) transforms directly to one dihydrate polymorph (DH-II). At 50 °C, AH transforms stepwise to a monohydrate (MH) then to the other dihydrate polymorph (DH-I). DH-II transforms to a tetrahydrate (TH) more readily than DH-I transforms to TH. Both dihydrate polymorphs transform to the same MH. The properties of the polymorphic dihydrate control the transformation pathways of sodium naproxen.